1. Field of the Invention
The present invention relates to a preparation method of alkyldichlorosilanes by directly reacting metallic silicon with a mixture of alkyl chloride and (i) hydrogen chlorides, or (ii) an alkyl chloride which can generate hydrogen chloride at the reaction temperature in the presence of copper catalyst.
2. Description of the Background Art
Since a preparation method of methylchlorosilanes by directly reacting metallic silicon with methyl chloride in the presence of copper catalyst was introduced in the U.S. Pat. No. 2,380,995, the synthesis of organosilicon compound in the current silicon industry is mostly based on the above skill. In the above reaction, a number of high boiling materials besides methylchlorosilanes are also obtained in small quantity. Also because the reaction rate and the purity of products depend on a large number of factors, e.g., the purity of the starting materials, the type of the catalyst and amount of the catalyst used, co-catalyst, the reaction temperature and pressure, the type of reactor used, the degree of silicon conversion etc., the reaction conditions for the methyl chloride reaction have been well established to obtain a title compound effectively. But still, the direct reaction of other alkyl chlorides than methyl chloride with metallic silicon has never been practiced on a large scale due to the decomposition of alkyl chlorides.
In 1955, Petrov and his co-workers reported the direct reactions of propyl chloride or butyl chloride with metallic silicon (A. D. Petrov, N, P. Smetankina, and G. I. Nikisshin. J.Gen.Chem. USSR, 1955, 25, 2305) and obtained propyldichlorosilane or butyldichlorosilane having a Si—H bond in low yields, but not dipropyldichlorosilane or dibutyldichlorosilane. The production of propyldichlorosilane and butyldichlorosilane indicates that the alkyl chlorides decomposed under the reaction conditions to give hydrogen chloride, and the alkyl chloride and hydrogen chloride simultaneously reacted with the same silicon atom.
Also, Yoshio Ono and his co-workers reported that vinyldichlorosilane or isopropyldichlorosilane could be synthesized by reacting a mixture of ethylene or propylene and hydrogen chloride with elemental silicon, but the yield was low. They also reported that isopropyldichlorosilane and normal propyldichlorosilane could be obtained by reacting a mixture of propylene and hydrogen chloride with activated silicon contact mixture containing 3% by weight of copper at 500°C. for 10 minutes (M. Okamoto, S. Onodera, Y. Yamamoto, E. Suzuki, Y. Ono, J. Chem. Soc., Dalton Trans., 2001. 71-78).
The present inventors found that organodichlorosilanes having Si—H bond could be obtained when a mixture of organic chlorides other than methyl chloride and hydrogen chloride is reacted with elemental silicon due to the reaction of both organic chloride and hydrogen chloride with the same silicon atom. For instance, when a mixture of methylene chloride and hydrogen chloride is reacted with silicon, one mole of methylene chloride and two moles of hydrogen chloride react with a same silicon atom to give bis(dichlorosilyl)methane (Jung et al., U.S. Pat. No. 5,235,083 (Aug. 10, 1993)). When a mixture of chloroform and hydrogen chloride is reacted with silicon, one mole of chloroform and three moles of hydrogen chloride react with a same silicon atom to give tris(dichlorosilyl)methane (Jung et al., U.S. Pat. No. 5,332,849(Jul. 26, 1994)). Similarly, when a mixture of allyl chloride and hydrogen chloride is reacted with silicon, one mole of allyl chloride and one mole of hydrogen chloride react with a same silicon atom to give allyldichlorosilane (Jung et al., U.S. Pat. No. 5,338,876 (Aug. 16, 1994)). In the above reactions, the decomposition of starting organic chloride was suppressed and products having Si—H bonds were obtained by adding hydrogen chloride as a raw material. Alkyl chlorides which can generate hydrogen chloride by decomposition at the reaction temperature could be also used instead of hydrogen chloride.
In a direct reaction of metallic silicon and organic chloride, it is well known that the reactions do not proceed without catalysts, and the preferred catalyst is copper. If necessary, metals as Zn, Al, Cd and the like can be used as a co-catalyst. If the amount of the copper catalyst is increased, the reaction becomes faster but the content of chlorine in products increases. Therefore, copper is generally used in about 10% or less by weight for the weight of silicon in the reaction of silicon and methyl chloride.
On the other hand, when methyl chloride was directly reacted with silicon, if metal complex of organic phosphin was added, methylchlorosilanes could be synthesized in a higher yield with an excellent selectivity (S. Ueno, T. Shinohara, M. Aramata, Y. Tanifuji, T. Inukai, K. Fujioka, U.S. Pat. No. 6,215,012(Oct. 4, 2001)). Also, since the reaction of silicon with alkyl chloride was an exothermic reaction, if the heat of reaction could not be efficiently controlled, or if a proper reaction temperature was not maintained, the reaction materials were coagulated and a partly overheated state was formed (A. L. Klebamskii and V. S. Fikhtengolts, J. Gen. Chem. U.S.S.R, 1957, 27, 2693). Furthermore, it was reported that a excessively high reaction temperature gave more by-products as well as the preferred alkyldichlorosilanes, thereby alkyl chlorides of starting materials and products were decomposed causing the deposition of carbon on the surface of silicon, and accordingly activity of silicon was rapidly decreased (J. C. Vlugter, and R. J. H. Voorhoeve, Conf. Accad. Lincei, Alta Tech. Chim. 1962, 81).
The common disadvantage of these methods arises from the facts that since the composition of the products are largely affected by the reaction condition, this condition must be carefully determined to obtain the desired products effectively; economic efficiency is degraded by the low yield; and raw materials are rapidly decomposed to give much amount of by-products. The present inventors of the invention have studied a method for preparing alkyldichlorosilanes in a higher yield with restraining generation of the by-products. As a result, the present inventors found an improved method for preparing alkyldichlorosilanes by directly reacting metallic silicon with a mixture of alkyl chloride and hydrogen chloride or alkyl chlorides which can generate hydrogen chloride at the reaction temperature.